Fly ash reclamation by pelletizing



Aug. 16, 1960 Original Filed May 19, 1949 FIG. 1

2 Sheets-Sheet 1 INVENTORS GEORGf 5. [8525015 3 BY warm 1 DUPL/MJR.

A-TTORNEY Aug. 16, 1960 v. .1. DUPLIN, JR, ETAL 2,948,948

FLY ASH RECLAMATION BY PELLETIZING 2 Sheets-Sheet 2 7 Original Filed May19, 1949 INVENTORS GEORGE E. EBEESOLEX wcro/e J oz/pu/v, JR. 3%

/ ATTORNEY tain some cenospheres.

included in operational expense. dustry has long sought for aneconomical method of United States Patent FLY ASH RECLAJMATION BYPELLETIZING Victor J. Duplin, In, Harrisburg, Pa, and George B.Ebersole, deceased, late of Westfield, N1, by Mabel G. Ebersole,executrix, Harrisburg, Pa., assignors to The Babcock &" Wilcox Company,New York, N.Y., a corporation of New Jersey Continuation of applicationSer. No. 94,184, May 19, 1949. This application Dec. 10, 1956, Ser. No.627,971

7 Claims. (Cl. 25-456) This invention relates to the reclamation offinely divided, normally waste, material and, more particularly to theformation of structurally stable lightweight granules or aggregates fromfinely divided waste material, such as fly ash, flue dust, ore dust,etc. While applicable generally to the processing of finely dividedmaterial of many types, the invention is particularly useful for thereclamation of finely divided coal ash. This application is acontinuation of our copendiug application Serial No. 94,- 184, filed May19, 1949, noW abandoned, for Method of and Apparatus for FormingFinely'Divided Material into structurally Stable Granules. I

Large capacity, pulverized coal fired boiler plants burn a large tonnageof coal daily, and the disposal of the residual ash represents a verydifiicult problem particularly 'weight result in a difiicult disposalproblem, as it is readily blown away by the wind when transported anddumped, creating a nuisance, and forms quicksand when dumped in swampyground.

The fly ash constitutes about 80% of the total ash, and has a finenessof the order of 90% through a 200 mesh screen. The particles aregenerally rounded and con- The bottom ash constitutes about 20% of thetotal ash and ordinarily contains little, if any,

carbon.

The trucking and dumping of the ash from a boiler plant is an expensivedisposal operation which must be The power plant inreclaiming the ash ina salable form that will at least reduce the disposal expense.

7 In accordance with the present invention, economically profitablereclamation is eifected by continuously pelletizing a moist mixture ofthe finely divided material and a lightweight, structurally stablegranules. These granules can be used as an aggregate in making concreteand the like, or can be formed into lightweight shapes for use asbuilding partitions. The aggregate and the shapes can be sold for acompetitive price suffici'ent to reduce substantially, and in some casesto eliminate, the ash disposal costs. 7

The bottom ash is screened to collect the finer particles, and these aremixed with the fly ash to form the basic raw material. This material isthen mixed with a suitable cheap binder and/or including a glaze-formingelement and formed into moist pellets having suflicient mass to avoidsticking when the damp pellets are high- 2 ly heated for a short time.in a hot reaction chamber. The heating burns out the carbonconstituents, generating gaseous products of combustion which expand thepellets to form voids and pores, while fusing the glaze-forming elementto form a glaze on the surface of the expanded pellets. The resultantgranules are then annealed to in crease their strength, after which theymay be used as an aggregate or formed into lightweight shapes (aboutlbs/culft.) which may be used for sound insulation or for partitions..The coarse material separated from the bottom ash is passed directly tothe finished granule stage. The binder also acts to lower the fusiontemperature of the entire pellet, so that the intense rapid heating at apredetermined high temperature also effects at least incipient fusion ofthe ash. e

In one form of apparatus for practicing the invention method, the basicmaterial is placed in a suitable proportioning'mixer where it isthoroughly admixed with a moist binder preferably having a glaze-formingconstituent with a fusion temperature lower than that of the rawmaterial. The dampened mixture is discharged into an elongated inclinedrotating tube, which cascades the mixture to form substantiallyspherical, damp pellets having substantial strength and stability. Thetube is preferably heated for at least its initial section to quicklyremove sulficient' moisture from the mixture to prevent excessivesticking to the tube surface to assist the pelletizing.

At the discharge end of the pelletizing tube, the pellets are screenedas to size, and fines and undersized pellets are returned to the mixerfor recycling. The still damp pellets above a predetermined size are fedinto a rotating kiln, where the damp pellets are quickly heated to ahigh temperature to burn out the carbon, drive off the entrappedmoisture and gases, and fuse the binder to surface glaze the pellets.The heating also effects at least incipient fusion of the ash. Due totheir substantially spherical shape, to the'vis'cous envelope, and totheir mass,

the pellets easily tear" themselves awa from the kiln surface, preventinsticking and the formation of a ringin the kiln. The quick, intense,heating transforms the pellets irito s'iflffed, structurany s't'abl,lightweight granules having a multiplicity of interior voids due to theburning out of the carbon and expulsion of the gases formed by heatingof the binder constituents. These granules are then slowly annealed in asuitable chamber to improve their strength'and toughness.

With the foregoing in mind, it is an object of the present invention toprovide a method of an apparatus for usefully reclaiming previouslywasted finely divided material. i

Another object is to provide a novel method of an apparatus for forming.structurally stable granules for use in building materials.

A further object is to provide a new lightweight aggreg'ate and newlightweight construction shapes;

These, and other objects, advantages and novel features of the inventionwill be apparent from the following description and the accompanyingdrawings. In the drawings: 1

Fig. 1 is a side elevation view, partly in section, schematicallyillustrating one form of apparatus with which the invention may bepracticed;

Fig. 2, is a view similar to Fig. 1 showing a modified pelletizingarrangement;

Figs. 3 and 4 are side-elevation views of diiferent ar rapid and intenseheating. This efiects the formation of structurally stable well knitpellets or granules within a definite size range to avoid excesiveexpense of crushing the finished product, and the pelletization controlsthe size of the feed to the heating apparatus to avoid dust therein oran excesive quantity of undersized pellets or granules. Additionally, inthe damp pellet form, the material can be rapidly and intensely heatedby passage through a short length hot furnace or kiln Without stickingof the material to the walls of the furnace or kiln, the formed pelletshaving sufficient mass and internal coherence that they easily breakaway from the furnace or kiln walls. To accomplish these results, thepelletizing operation provides for thorough admixing of the finelydivided material with a moist binder, or with a dry binder and theadidtion of moisture, both preferably having a glaze-formingconstituent, which allows such intense rapid heating of the pelletswithout disintegration and reduces to a minimum the escape of dust fromthe heating apparatus.

The initial or raw material may be any finely divided, normally wastesubstance, such as ash from coal fired boiler furnaces or dust from anyprocessing operation,

such as blast furnace flue dust, ores, etc. To provide for adequatepelletization, the fineness of the material is limited to substantiallynot more than 20% passing through a /8 mesh, in the case of fly ash, andthe balance to be 80% to 90% passing through a 200 mesh screen.

' Percent SiO 45-50 A1 27-35 F6203 4 C 412 CaO 2-3 i Miscellaneous 9 Theash, after having been screened as to size, is mixed with a suitablebinder either before or during the pelletizing step to form a moistmixture. The material added as a binder and/or expander is preferablyone having solid glaze-forming constituents having a fusion temperaturesubstantially lower than the relatively high fusion temperature of theash. Thereby, the binder is fused during the rapid intense heating stepto quickly form a viscous glaze or envelope on the pellets, binding orcementing the latter against disintegration due to the subsequentexpulsion of the internal gases and burning of any pellets so that theheating effects at least incipient fusion of the ash. The binder alsolowers the fusion temperature of the parent material. The primarypurpose of the binder is to assist the ash to pelletize and to retainthe pellet shape when the latter is dropped into the vheating apparatus.

The following materials are suitable as binders and expanders: Clays,such as bentonite or "suitable local ball clays, limestone, Semet Solvaywaste, sodium chloride, combinations of Semet Solvay waste and sodiumchloride, pulverized pyrites and slate rejected from coal pulverizers(which substances are also a source of fuel),

water, borax, soda ash, aluminum sulphate, sodium sulphate, calciumsulphate, calcium chloride, plaster of Paris, sodium carbonate, calciumcarbonate, boric acid, and various organic binders, such as dextrine,starch, flour, sulphite liquor waste and Wood flour. All the abovematerials act both as binders and expanders, and

f mixer.

all of these materials, except the water and the organic binders, areglazed formers.

By the term Semet Solvay waste as used herein is meant a material havingsubstantially the following com.- positions:

During the processing according to this invention, the

carbon burns out and, with the addition of Solvay waste and salt (NaCl),more lime (from the Solvay waste) and alkali (Na O) are added. Both ofthese are fluxes which lower the fusion temperature and thus allow themass to sinter and develop strength at a lower temperature. The

amount added is sufiicient to efiect sintering of the mass at theprefered firing temperature which is of the order 'of 2200 F.

,During the treatment, the sulphates and carbonates decompose intooxides and evolve gases which assist bloating of the mass (for lowdensity) when the pellet surface is sealed with a glaze or glass. As thegases developed within the envelope tend to expand the mass, it isadvantageous to heat the pellets rapidly to seal the surface quickly.

The salt (NaCl) melts at 1472 F. and tends to vaporize at 2200 F. Thissalt reacts with the ash to pro- :duce a typical salt. glaze condition,and also to form a glassy silicate at and above the salt melting point.The

lime and alkalies from the Solvay waste tend to form glass silicates ofthe soda-lime type, and also lower the fusion temperature.

The ash and the binder may be premixed either by dry mixing or by wetmixing. The latter is preferred due to thedecreased dust-ing and bettercontrol afiorded thereby. In dry mixing, the ash and the binder may beted by a proportioning hopper, poidometers, or vibrating feeders into acontinuous pug mill, or may be mixed by a dry batch process in a ribbontype mixer and discharged into a hopper from which the mixture is fed to'the pelletizer at a controlled rate.

There are several methods by which the ash and the binder may be wetmixed. In one method, the mixture is Wetted by a spray as it passesthrough a pug mill type In another method, described more fullyhereinafter, the ash and binder are mixed directly in the pelletizingtube by feeding the dry ingredients thereto at a controlled rate andspraying the dry mixture with a controlled water spray while rotatingthe tube. Other suit- 'able wet mixing methods involved mixing the ashand binder with Water in a rotating drum and feeding the mixturedirectly into the forming tube, or mixing the ash and binder with apredetermined quantity of Water in a rotating drum followed bypelletizing the mixture directly in the mixer.

The preferred method of pelletizing is to feed the damp mixture into arotatable cylindrical pelletizing tube which has an inclination whichcan be varied, but which is preferably maintained at about 3%. Thepelletizing tube is externally heated for its initial section, forexample for about /3 the distance from its entrance, and a quantity ofair is passed through the tube to remove moisture depositing on the tubeas the damp material is cascaded through the tube to form pellets.

The operationis shown, as a whole, in Fig. l of the drawings, whereinbins 1i and 1 1 are shown as arranged to receive the ash and the binder,respectively. The two materials are fed from the bins by proportioningfeeders (not shown) so that the correct proportions of raw material andbinder are delivered to a mixer feeder 12. The latter delivers the mixedmaterial to a discharge chute 13 extending into the feeding end of apelletizing tube 15. A by-pass chute 14 is provided for receiving thematerial when the pelletizing apparatus is out of service for repairs ormaintenance, for example. a

A water line 16 is provided for furnishing the mixing water for wetmixing, and water may be fed to mixer feeder 12 through branch 17, or totube 115 through branch 18 and spray head 19. The water from branch 17may be used to mix with clay, when the latter is used as a binder, or aconvert the usual filter cake of Semet- Solvay waste into a pumpableslurry, which is used as a binder for mixing with the raw material.

As the mixture is discharged into tube 15, a thin coating is formed onthe inside of the tube, such coating being limited in thickness by ascraper, or the like, as described hereinafter. Additionally, heating ofthe tube 15, in a manner described hereinafter, and passing of airtherethrough, assist in limiting the thickness of the coating. Frictionbetween the damp material and the coated tube is suflicient to cause thematerial to cascade as tube is rotated, and due to the inclination ofthe tube. As the mixture 20 cascades upon itself, it rolls intosubstantially spherical pellets 30 of varying sizes.

At the discharge end of tubes 15, a rotatable screen 21 receives thedamp pellets discharged from tube 15 as well as any unpelletizedmaterial 20. The pellets below a predetermined size, as well as anyunpelletized material, pass through screen 21 into a hopper 22 leadingto a horizontal conveyor 23. A vertical conveyor 24 receives materialfrom conveyor 25 and carries it to the entrance of discharge chute 13for recycling through pelletizing tube 15,

The formed pellets equal to or greater than such predetermined size arepassed over screen 21 to a hopper 26 having a discharge tube 27 leadingto a rotary furnace or kiln 25. immediately upon. their entrance intokiln 25, the pellets are quickly highly heated causing a substantiallyinstantaneous evaporation of moisture. As the moisture moves to thesurface of the pellets, it carries with it the binder glaze-formingconstituents which are in solution, and these constituents, as theyapproach or. reach the highly heated pellet surface, melt. Theglaze-forming constituents originally at the surface also melt. Thismelting provides a viscous envelope for the pellets, consisting ofmelted glaze-forming constituents interconnecting ash particles. Thisviscous envelope is semi-fluid.

As the heating of the pellets continues, the carbon content of the ashburns out providing additional heat and producing voids having nearlythe same volume as the unburned carbon, and chemical reactions -occur inthe binder constituents evolving gases. Some of this carbon burning andchemical reaction takes place at the pellet surface, as well asinternally. The resulting gases are driven off through the viscoussurface envelope, forming a multitude of interconnected voids andsurface pores, so that a porous cellular structure results. The steamfrom the evaporated moisture also takes part in the void and poreformation.

Further heating of the pellets results in at least incipient fusion ofthe ash particles and the transformation of the glaze-forming binderconstituents into a glass like structure. interconnecting and bondingthe ash particles and forming enclosures for the voids. The viscous.surface envelope likewise becomes glassy. During this time, the

- pellets 'roll along the kiln wall and the surface envelope,

in combination with the. mass and substantially spherical shape of thepellets, assists the pellets in tearingthemselves loose from the kilnWall. The resultant structurally stable lightweight granules aredischarged into an in the binder appears to be as follows.

annealing pit or chamber 35 where the granules are slowly annealed toincrease their strength and toughness;

The action of the glaze-forming materials in solution When the pelletsare rapidly and intensely heated, the water is driven out of the pelletsat a high rate. As soon as most of the water is gone, the water solublematerial is transported close to the pellet surface, and some of thematerial at the surface melts. The surface tension of the meltedmaterial holds the fly ash particles together until the pellet surfacetemperature is sufliciently high to form a ceramic bond. 7 g

Kiln 25 is heated by a'suitable fluid fuel burner 28 at its dischargeend. To improve the heat economy of the apparatus, the hot gases fromkiln 25 are utilized in a steam boiler unit 31 comprising a boiler 31aand an economizer 31b and having a row of screen tubes 32 across the gasexit from kiln 25 which, together with roof 33 and roof tubes 34,support discharge spout 27. Spout 27 is thus highly heated which assistsin preventing the damp pellets 30 sticking therein while beingdischarged to kiln 25. The gases from boiler 31 pass through a dustcollector 36 to a stack 37. Dust collector 36 dis charges into aconveyor 38 which also receives material from the hoppers 39 of boiler31. Conveyor 38 returns the collected materialto hopper 10 forrecycling; Best results are obtained when the pellet surfacetemperatures in the kiln range from about 1300 F. to about 2250 F., withthe idealtemperature dependent upon the particular binder, as will benoted in the examples appearing hereinafter. I

In the operation of the apparatus of Fig. 1, all material less thanabout 4-mesh is recycled. If pellets fed to kiln 25 are too small insize, they tend to stick to each other and to the kiln walls forming aring which prevents free pellet flow through the kiln and which must bebroken up to restore the pellet flow. This excessive agglomeration inthe kiln, characteristic of undersized pellets, deter- 'mines the lowersize limit of the pellets fed tokiln 25.

On the other hand, pellets which are too large in size are notsatisfactorily bonded in the kiln due to the limitations of-theavailable heating time in a continuous process. Consequently, the uppersize limit of the pellets'is' determined by the thermal conductivity ofthe pellets and the available heating time in kiln 25. The oversizedpellets may be rejected by a suitable screen in advance of the kilnentrance. By recycling the fines and undersized pellets, these may bebuilt up to the desired minimum size.

The desired form of furnace 25 is a short kiln of large diameter with arelatively steep slope and rotated at a relatively high speed to movepellets 30 quickly through the kiln. The pellets must have sufficientstrength to avoid breakage when fed to kiln 25, and the pellettemperatures must be quickly raised to a temperature sulficient toeffect surface glazing of the pellet to avoid drying and disintegrationinto dust. This dust will cling. to the kiln surface, forming a ring,which effect is also caused if too high a percentage of small pellets isadmitted to the kiln. Y Y

The nature and composition of fly ash is such that,

when mixed with a binder and intensely heated at the temperature presentat the entrance .to kiln 25, an amorphous glass will be developed in thestructure of the granule as described hereinabove, particularly whenglass-forming binder constituents are present. If the granules are notcooled slowly, the incipiently fused ash will he brittle and developnumerous fine cracks tending to decrease its strength. Consequently, thehot granules 30 discharged from kiln 25 must be cooled slowly in pit orchamber 35 in a manner similar to the annealing of glass.

While many types of binders are suitable, the following examples willserve to illustrate typical mixtures which have proved successful inpractice.

Water sausage.

Water 7 Example 1 Parts Fly ash 80 Bottom ash 20 Salt (NaCl) 5 Water 20The materials were wetted and agitated to form the pelletizing mixture.The formed pellets were intensely heated in the kiln at a pellet surfacetemperature of about 2125 F. to form a sausage of adhering pellets.There was no disintegration or dusting, and acceptable structurallystable granules were obtained. The kiln temperatures in this and in thefollowing examples were approximately 150 F. higher than the pelletsurface These materials were mixed as in Example I, pelletized and fedto the kiln. At about 1900 F. pellet surface temperature, there was nodisintegration or dusting in the kiln and, at about 2260 F., the pelletsformed a Acceptable, structurally stable, lightweight granules wereobtained. It is to be noted, from the composition given above, thatSemet Solvay waste is a source of lime.

Example III Part-s Fly ash 80 Bottom ash 2.0 ,Semet Solvay waste (seeanalysis above) 5 When these materials were mixed and pelletized, hard.

firm pellets were formed. When these pellets were fed to the kiln andquickly heated to about 2200 F. pellet surface temperature, theyexploded. The explosive disintegration of the pellets stopped when thepellet surface temperature at the kiln entrance was lowered to about1975 F. with the pellet feeding being continued.

, At about 2020 F. pellet surface temperature, the pellets rolled freelyin the tube but, when the temperature was increased to about 2160 F.,the pellets began to become sticky. Lowering the pellet surfacetemperature to about 2070 F. restored the free rolling of the pellets,and commercially satisfactory, structurally stable granules wereproduced.

To prevent excessive building up of the mixture on the surface ofpelletizing tube 15, it has been found that heating tube 15, incombination with the use of an interior scraper, is etfective. Oneeffective way of providing such heating is shown in Fig. 2, wherein tubeis heated by hot boiler gases induced to flow upwardly through a heatingchamber 40 surrounding tube 15, by the fan 37 of dust collector 36. Coldair is drawn through tube 15, to remove excess moisture, by a bypass 41connected to the discharge end of tube '15 and leading to discharge endof conduit 42. a

In this case, the raw material and the binder are fed to a hopper 44discharging into mixer feeder 12 which feeds the mixture directly totube 15 through an entrance grating 46. The rejected fines from screen21 *'-and hopper 22 are returned to hopper 44 through the medium of abulk conveyor 47. Except for the described 8 differences, the apparatusis otherwise the same as that ofsFig. 1 although it may be used withequal facility with the stack for the main furnace or furnaces of aboiler plant.

Fig. 3 illustrates, in somewhat greater detail, the support and drivingarrangement for pelletizing tube '15, and a mixture feeding arrangementtherefor. The particular tube shown in this figure is an 18 inch sheetmetal tube, 14 feet long and having a 3 30 slope. The tube 15 is mountedon rollers 56 on supports 57, and is driven by a motor 58 through aspeed changer 61 and gearing 62, at approximately 30 to 50 r.p.m.

In Fig. 3 the dry materials are mixed in proportioning hopper 50 and fedthrough pipe 51. A water spray pipe 63 extends into tube 15 and issupplied with water from "a pipe 64 through a filter 66, a rotameter 67and a control valve 68. As seeninFig. 3A, a longitudinally arrangedelongated scraper 69 is provided to keep the internal coating of thetube at a predetermined optimum thickness.

In this case, the dry materials are subjected to a fine water spraywithin-the initial length of the tube. The water droplets form smallpellets as they fall into the dry material, and these pellets areenlarged and compacted as they cascade through the length of the tube.The Water spray method of Fig. 3 requires critical control of both thewater spray and the dry feeding of the mixture. The spray must be solocated that all the droplets fall into the tumbling bed of fly ash, as,if the spray wets the tube wall, a quantity of flay ash will adhere tothe wall and eventually b ecome too wet.

A preferred form of pelletizing tube 15 is shown in Fig. 4 as beingconsiderably longer than the tubes of Figs. 1 and 3. Tube 15, may be,for example, an 18 inch diameter, 3 section, steel tube, 30 feet longand having a pitch of 1 inch in 6 feet. Tube 15' is supported on rollers71 on supports 72, [and a motor 73, through a belt drive 74, rotates thetube at about 51 rpm. At the discharge end, rotating screens 76 separatethe pellets ranging from 8 mesh to /2 inch for firing in the kiln. Thefiner pellets and the unpelletized material are recycled. Tube 15' isfed with a wet mix through discharge pipe 13, and the first 10 footsection of the tube is heated by suitable means, schematically indicatedas gas burners 77 although other heating arrangements, such as that ofFig. 2, may be used. A stream of air is introduced through the tube bymeans of a forced draft fan at the discharge end (not shown) to removemoisture from the tube surface. The pellets produced are superior tothose produced by the pelletizing tube arrangement of Figs. 1 and 3,although these latter produce commercially satisfactory granules.

Incipient fusion of the ash is efiected more readily in a kiln having acontrolled atmosphere, which is preferably reducing in nature, andcontrolled tempenatures throughout its length. By control of thesefactors, particularly the temperature, the density of the granules maybe closely controlled in accordance with desired values of expansion orof density. For example, if the kiln temperatures are maintainedsufliciently high, the rash may be fused to a greater extent to providea harder and more dense fused, glass-like structure. With the pelletsurface temperature values given in the foregoing examples, an expanded,lightweight, low density product is produced.

An even greater degree of bloating or expansion of the pellets can beobtained by subjecting the latter to additional sudden intense heatingas the granules are discharged from the kiln. Such additional heatingmay be effected by arranging another burner so as to produce a shorthighly heated zone at the discharge end of the kiln. Control of the kilnatmosphere and temperatures gives a control of the color of the granulesso that a commercially satisfactory product, from the color stand point,is provided.

An approximate analysis of the final product is as follows:

With the described process, the formed pellets retain their identity andare expanded to provide the multicellw lar structure while the visousenvelope formed by the surface glaze is still in a semi-molten state.Nevertheless, the pellets retain suflicient mass to break away from thekiln lining and progress toward the discharge end. Since the pellets aresubstantially spherical, their areas of contact with the kiln oradjacent pellets are limited, which facilitates the break away andinhibits undue agglomeration. However, to assure these desirableeffects, close control of the pellet size is necessary.

As a specific example of results achieved by the present invention,gnanules produced by the described process have been crushed and used asan aggregate to form a cinder block of the usual hollow type having, forexample, 4 webs defining three compartments. A low ratio cement mixture,comprising 8 parts of crushed granule aggregate to one part of cement,produced an 8x8xl5 block having a weight of 26 /2 lbs. and a crushingstrength of 800 lbs., the block density being about 53 lbs/cu. ft. Thiscrushing strength compares with a value of 690700 lbs. for the same sizeand type of block produced from prior art aggregates. The weights mayrange from 26 to 27 lbs., and the densities from 50 to 55 lbs/cu. ft.,although this range may be made 40 to 60 lbs with proper additions andfiring control.

While specific embodiments of the invention have been shown anddescribed in detail to illustrate the application of the inventionprinciples, it should be understood that the invention may be embodiedotherwise Without departing from such principles.

What is claimed is:

1. For use in an aggregate for forming a low density structural shape,burned lightweight granules each consisting of coal ash bonded by aglaze forming binder containing NaCl and having -a fusion temperaturelower than that of the coal ash, each granule consisting of from 80 to100 parts by weight of coal ash glazed and bonded 5 parts by weight ofsuch binder; the binder before burning having the following compositionby weight:

Parts H O 57.0 CaCO 26.0 CaO 4.0 MgO 0.5 CaCl 4.0 CaSO 1.5 NaCl 1.251520( 5.00

2. A method of agglomerating finely divided particles containingcombustible matter, to form an aggregate, comprising, in combination,providing a moist mixture of the particles and a binder including awater soluble glaze-forming constituent forming a ceramic glaze whenheated to a temperature in excess of 2000 F.; forming the damp mixtureinto pellets; and, in a single, continuous and uninterrupted operationrapidly and intensely heating the damp pellets to a pellet surfacetemperature of at least 2000 F. to generate steam from the moisture withthe water soluble glaze-forming constituent carried toward the surfaceof the pellets and to burn out the combustible matter within the pelletswhile fusing the binder to bond the particles and form a ceramic glazeon the surface of the pellets, to form structurally stable low densitygranules having a multiplicity of 'voids therein.

3. A method as claimed in claim 2 in which the pellets are heated in areducing atmosphere.

4. A method as claimed in claim 2 in which the binder has a fusiontemperature lower than that of the particles.

5. A method as claimed in claim 2 in which the binder includes sodiumchloride.

6. A method as claimed in claim 2 in which the binder includes sodiumchloride and lime.

7. A method as claimed in claim 2 in which the particles are fine ashincluding fly ash.

References Cited in the file of this patent UNITED STATES PATENTS1,741,574 Kraus Dec. 31, 1929 1,967,311 Kern July 24, 1934 2,268,816Gabeler et al. Jan. 6, 1942 2,478,757 Foster Aug. 9, 1949 2,543,898 DeVaney Mar. 6, 1951 UNITED STATES PATENT OFFICE CERTIFICATION OFCORRECTION Patent No! $948,948 August 16, 1960 Victor J. Dulplin Jr. Yet a1 It is hereby certified that error appears in the above numberedpatent requiring correction and that the said Letters Patent should readas corrected below.

In the grant, lines 1 and 2 for "Harrisburg,

Pennsylvania read Fanwood, New Jersey in the heading to the printedspecification line 3, for "Harrisburg, Pas," read Fanwood N;. L, column5, line 16 for or a read or to Signed and sealed this 25th day of April1961,

(SEAL) Attest:

ERNEST W. SWIDER DAVID L, LADD Attesting Officer Commissioner of Patents

